Method and apparatus for capacity-efficient restoration in an optical communication system

ABSTRACT

A method and system provide capacity-efficient restoration within an optical fiber communication system. The system includes a plurality of nodes each interconnected by optical fibers. Each optical fiber connection between nodes includes at least three channel groups with different priority levels for restoration switching in response to a connection failure. The system maintains and restores full-capacity communication services by switching at least a portion of the channel groups from a first optical fiber connection to a second optical fiber connection system based on the priority levels assigned to the channel groups. Service reliability is effectively maintained without incurring additional costs for dedicated spare optical fiber equipment by improving idle capacity utilization.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to optical communicationsystems. It particularly relates to a capacity-efficient restorationarchitecture for an optical communication system.

[0003] 2. Background Art

[0004] The operations, administration, maintenance, and provisioning ofoptical fiber communication systems are described in the SynchronousOptical Network/Synchronous Digital Hierarchy (SONET/SDH) standards asspecified by American National Standards Institute (ANSI) andInternational Telecommunication Union-Telecommunication StandardizationSector (ITU-T). SDH is specified in ITU-T G.707 Recommendation, Networknode interface for the SDH.

[0005] Typical optical fiber communication systems comprise acombination of transmitters, receivers, optical combiners, opticalfibers, optical amplifiers, optical connectors, and splitters.Wavelength Division Multiplexing (WDM) or Dense Wavelength DivisionMultiplexing (DWDM) systems also comprise couplers to enable multiplewavelength transmission over the same optical fiber. Typical opticalsystem configurations include mesh networks and ring networks. Ringnetworks commonly comprise two fiber pairs connecting a plurality ofnodes in a loop. One fiber pair carries bi-directional aggregate trafficbetween pairs of nodes in the ring. The second fiber pair is used tore-route traffic when there is a failure in the ring on a shared basis.A two-fiber ring is also available in which half the capacity within afiber is reserved for traffic restoration. Mesh networks commonlycomprise a plurality of nodes wherein a node can be connected to morethan two nodes in the network enabling enhanced network reliability andhigher capacity efficiency when a link failure occurs.

[0006] Optical fibers carry far greater amounts of information thancarried by other communication media (e.g., electrical cables). Underthe Synchronous Optical Network (SONET') standard, the commonly usedOC-48 protocol operates at 2.488 Gbps supporting a capacity equivalentto over 32,000 voice circuits. The next highest protocol, OC-192,operates at 9.953 Gbps supporting a capacity equivalent to over 128,000voice circuits. Therefore, robustness and reliability is required fromsuch high-capacity, long-haul systems. Indeed, most Transatlantic cablesystems (TAT), undersea systems which carry internationaltelecommunication traffic, are required to have at least 25 yearreliability.

[0007] However, since reliability is never absolute most optical systemsrequire a restoration scheme to maintain some level of systemperformance despite fiber outages, amplifier failures, and some otherequipment failure. Several common restoration schemes commercially usedinclude those specified in the SONET standard in a point-to-point singlelink configuration or a ring network configuration.

[0008] Examples of these standardized traditional protection schemes areshown in FIGS. 1, 2. Particularly, FIG. 1 shows a typical one-linepoint-to-point 1:1 protection system in a Dense Wavelength DivisionMultiplexing (DWDM) scheme wherein nodes A, B are linked nodes within anoptical fiber communication system. The system shown operates inaccordance with the SONET/SDH standard, the standard for synchronousdata transmission on optical media.

[0009] The protection system architecture 100 includes protectionswitches 110, 190, working and protection link 150, and dense wavelengthdivision multiplexers (DWDMs) 120, 160. Working and protection link 150commonly comprises a single or multiple (cable bundle of fibers) opticalfiber connection between nodes A, B. Protection switches 110, 190commonly comprise optical-to-electrical transducers and/or optical layercross-connection switches that provide communication serviceconnectivity between the protection system 100 and other communicationdevices (e.g., customer premises equipment). There exists a one-to-onecorrespondence between working channels (lines) 130, 170 and protectionchannels (lines) 140, 180. However, both working and protection channels130, 170, 140, 180 are multiplexed by the DWDMs on to a single opticalfiber connection between DWDMs 120, 160 for one direction (e.g., A toB). Another corresponding fiber is typically used for the otherdirection traffic from B to A.

[0010] In response to a failure in the transmitter or receiver orcabling for a working line, the SONET/SDH signals carried by workinglines 130, 170 are switched from the working lines 130, 170 to theprotection lines 140, 180 by protection switches 110, 190. However,since both working lines 130, 170 and protection lines 140, 180 arecarried by the same working and protection link 150, a fiber cut in link150 or a failure in DWDMs 120, 160 or in an optical amplifier for link150 completely terminates optical communication services between nodesA, B over link 150. To resume service, alternate routing (not shown)would be necessary that can be accomplished through ring switch or meshrestoration means.

[0011]FIG. 2 shows the same protection configuration but now with atwo-line point-to-point 1:1 protection architecture 200. The protectionsystem architecture 200 includes protection switches 210, 295 workinglink 250 and protection link 260, and DWDMs 220, 270. DWDMs 220, 270multiplex working lines 230, 280 and protection lines 240, 290 on toseparate working link 250 and protection link 260 between nodes A, B.

[0012] For this protection scheme, in response to a failure in thetransmitter or receiver or cabling for a working line as well as anoptical amplifier or DWDM failure, the SONET/SDH signals carried byworking lines 230, 280 are switched from the working lines 230, 280 tothe protection lines 240, 290 by protection switches 210, 295. However,again, to resume service when both working and protection links 250, 260both fail or are cut because the fibers in lines 250 and 260 are in thesame cable, alternate routing (not shown) would be necessary that can beaccomplished through ring switch or mesh restoration means.

[0013] Both 1-line or 2-line 1:1 DWDM systems shown in FIGS. 1, 2 areinefficient in terms of utilization of protection capacity. Both systemsuse 100% idle capacity that either does not generate any revenue orprovides low-grade service on the protection lines. This low-gradeservice can be preempted when there is a failure of the primaryrevenue-generating service.

[0014]FIGS. 3, 4 again show a commonly-used optical restoration systemarchitecture that provides communication services in accordance with theSONET standard. Particularly, FIG. 3 shows a one-line 1:N protectionsystem using DWDM. The protection system architecture 300 includesprotection switches 310, 390 working and protection link 350, and DWDMs340, 360. Nodes A, B within the system are interconnected by working andprotection link 350. In the 1:N protection scheme, there is onededicated protection channel (line) 330, 380 for each group of N (N>1)working channels (lines) 320, 370. A typical example may be ten groupsof 4 (N=4) working channels therein resulting in 10 protection channelsfor a total number of 40 working channels. In the illustrative exampleshown in FIG. 2(a), a transmitter/receiver failure on one of a group ofN working channels 320, 370 is protected by switching to a protectionchannel 330, 380 dedicated for that group. Again, due to the one-linescheme for working and protection link 350, an optical amplifier failureor fiber cut results in a termination of communication services betweennodes A, B over link 350. Working channels 320, 370 must be re-routedusing a ring or mesh restoration network (not shown).

[0015] Similarly, FIG. 4 shows a two-line 1:N (N>1) protection systemusing DWDM. The protection system architecture 400 includes protectionswitches 410, 495 working link 450 and protection link 460, and DWDMs440, 470. Nodes A, B within the system are interconnected by workinglink 450 and protection link 460. For a DWDM or optical amplifierfailure, or fiber cut even in a two-line DWDM configuration, (N−1)channels from each group of N working channels 420 will not be restored.Therefore, in our current example assuming ten groups of 4 (N=4) workingchannels, there are only 10 restoration channels resulting in 30channels [(N−1)*10] not being restored.

[0016] Additionally, even a 2-line 1:N protection using DWDM does notefficiently utilize idle capacity. When the working DWDM link 450 isused to its maximum capacity, only 1/N fraction (e.g., ¼ fraction forcurrent example) of the working channels 420 is used in the protectionDWDM link 460 thereby not utilizing the protection DWDM link 460 to itsmaximum capacity. Therefore, the two-line 1:N protection systeminefficiently utilizes the capacity of the protection link although itis more capacity-efficient than the two-line 1:1 protection system whichhas 100% idle capacity. However, the two-line 1:1 protection systemoffers better reliability as all working channels in the failed workinglink will be effectively switched to the idle protection link ascontrasted to the 1/N protection capability of the two-line 1:N system.

[0017] Another category of restoration schemes include systems which arenot confined to a single link. These systems include Bi-directional lineswitched rings (BLSR) and mesh restoration. These systems have theadvantage that the protection capacity is utilized on a shared basis forfailures in multiple links within the ring. Particularly, BLSRstypically comprise four fiber rings wherein traffic in one directiontravels on one fiber pair while traffic in the opposite directiontravels on the other fiber pair. This scheme uses 1:1 configuration foreach link of the ring, but the same protection lines of the links of aring are also used for protection against a fiber cut type of failurewhen both working and protection lines of another link fail. Forfailures which affect only the working channel on a route, the signal isprotected by using the 1:1 protection scheme previously described. Forfailures that affect both the working and protection lines of a route,the signal is restored using the protection line carrying traffictraveling around the other direction of the system. The same protectionline is used on a shared basis when both working and protection channelsfail anywhere within the ring. It would require much more capacity toprovide similar reliability as a BLSR against fiber cuts using a 1:1protection scheme. In the 1:1 scheme, the working line and theprotection line between any pair of protection switch systems need to berouted via DWDMs in the opposite directions in the loop.

[0018] However, the BLSR system still does not offer the most capacityefficient network when typically there are more than two fiber routes atmost of the nodes. This system is limited to particular applications andto only two types of service grades due to the two-fiber architecture.These two grades are the fully-protected service on the working channelsin a fiber or the pre-emptable service carried by the protectionchannels.

[0019] A mesh restoration scheme offers some additional advantage bysharing the protection capacity more efficiently than BLSR. Meshrestoration offers 1-line or 2-line 1:1 protection for each link or somemesh restoration architectures use a 1:N protection scheme for eachlink. The protection channels are also used for restoration against alink failure. Again, 1:1 protection makes inefficient use of protectioncapacity while 1:N protection offers lower reliability for workingchannels or poor utilization of DWDM capacity in 2-line 1:N protectionconfiguration.

[0020] In view of the above, there is a need to maintain capacitywithout incurring additional costs when restoring optical communicationlinks. Idle capacity utilization needs to be improved while providingmultiple grades of protection (varying priority levels) for differenttype of communication services. Due to the disadvantages of priorrestoration techniques, there is a need to restore communication linksand paths while still limiting costs and still maintaining capacity. Thepresent invention describes such a capacity-efficient restorationarchitecture that dynamically restores failed optical communicationlinks without incurring costs from idle protection links while stillmaintaining the same capacity or in some instances actually improvingcapacity from the failed link.

SUMMARY OF THE INVENTION

[0021] The present invention overcomes the previously mentioneddisadvantages by using a hybrid protection architecture for an opticalcommunication system comprising a plurality of interconnected nodes. Theprotection scheme uses a two-line optical fiber connection for each linkbetween nodes but is not 1:1 protection. At least three channel groupsare carried by each line wherein each channel group is assigned adifferent priority level for restoration. In response to a failure on aline, channels are switched in descending priority level to availablerestoration channels on another line or link to maintain opticalcommunication services connectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a block diagram of a one-line 1:1 protectionarchitecture for a known optical communication system.

[0023]FIG. 2 is a block diagram of a two-line 1:1 protectionarchitecture for a known optical communication system.

[0024]FIG. 3 is a block diagram of a one-line 1:N protectionarchitecture for a known optical communication system.

[0025]FIG. 4 is a block diagram of a two-line 1:N protectionarchitecture for a known optical communication system.

[0026]FIG. 5 is illustrates an embodiment of the present inventionshowing a representative hybrid protection architecture for an opticalcommunication system having a single failure

[0027]FIG. 6 illustrates an embodiment of the present invention showinga representative hybrid protection architecture for an opticalcommunication system having multiple failures

DETAILED DESCRIPTION

[0028] The present invention provides a hybrid protection architectureto efficiently restore optical communication services within an opticalcommunication system. The optical communication system preferablyoperates using the SONET/SDH standard. Therefore, it is noted thatparticular non-critical aspects of the standard and opticalcommunication system are not described in great detail as they are notcritical to the present invention and these aspects are well-known inthe relevant field of invention. Also, it is noted that those skilled inthe art will appreciate that the present invention may be equallyapplied to any optical communication system topology that comprises aplurality of interconnected nodes utilizing any communication format.

[0029] In reference to FIG. 5 and FIG. 6, optical fiber communicationsystems 500, 600 using a representative hybrid protection architecture(HPA) in accordance with the present invention are shown. The systems500, 600 comprise a plurality of interconnected (linked) nodes A, B, C,D. It is noted that nodes A, B, C, D are shown as a representativenumber of nodes and the invention is not limited to this particularnumber of nodes. The HPA uses a multiple-line optical fiber connectionfor each link between nodes, but the protection scheme is not 1:1.

[0030] Particularly, in FIG. 5, optical fiber communication system 500uses the representative HPA for a single interface (line) failurebetween node A and node B. The system 500 includes optical layercross-connect switches (OLXC) 505, 535, 560, 585 for each node A, B, C,D respectively. For both FIGS. 5 and 6, generally the OLXC can provide aplurality of functions as needed by particular communicationapplications. This functionality includes, but is not limited tofunctioning as a primarily optical domain switch wherein opticalcommunication signals switched by the OLXC do not undergo any conversionto the electrical domain, or functioning as an optical switch includingoptical and electrical components for any necessary conversion(optical-to-electrical or electrical-to-optical) of the switched opticalcommunication signals.

[0031] Referring again to FIG. 5, nodes A, B, C, D comprise interfaceequipment (IEs) 510, 515, 530, 540, 555, 565, 580, 590 with at least twoIEs for each node A, B, C, D respectively. At every node, each IEincludes at least two pairs of interface ports wherein one port in eachpair is used for interconnecting the IE to the OLXC while the other portin each pair interconnects the IE to another IE at a different node. TheIEs are interconnected to the OLXCs, via OLXC equipment cards at theOLXC end and the interface ports at the IE end, through a pair ofoptical fibers for carrying bi-directional traffic (e.g., OC-48 orOC-192 channels) or through electrical lines using optical-to-electricaltransducers. Advantageously, the IEs comprise wavelength divisionmultiplexers (WDM), preferably dense wavelength division multiplexers(DWDM).

[0032] Each IE includes a two-line optical fiber connection (link), viathe interface ports, to a separate node in the system 500 wherein lines520, 525 connect IEs 510, 530 for link AB, lines 545, 550 connect IEs540, 555 for link BC, lines 570, 575 connect IEs 565, 580 for link CD,and lines 595, 598 connect IEs 515, 590 for link AD. The lineconnections preferably comprise a single or multiple fiber (cable bundleof fibers) connection between nodes.

[0033] As shown in FIGS. 5 and 6 and the accompanying legends, eachline, interconnected to the optical layer cross-connect switch at eachnode, carries multiple channel groups using the DWDMs. These channelgroups preferably include super premium channels (SP), standard channels(S), and restoration channels (R). Both SP and S channels aretraffic-carrying (revenue generating) channels carrying high-speedtraffic (e.g., OC-48, OC-192) within the system which are protected andrestored against failures using the R channels. R channels are channelsof equivalent capacity to SP and S channels that are used to restorecommunication services carried by SP and S in response to failures inthese channels. These failures include, but are not limited to singlechannel failures, optical amplifier failures, transmitter and receiverfailures, interface port failures, and fiber cuts occurring on theoptical fiber channel connection between nodes. Also, R channels carrycommunication services that can be preempted in response to a SP or Schannel failure.

[0034] In both FIGS. 5 and 6, the OLXC switches the channels in event offailure. Generally, any network fault detection technique may be used totrigger the restoration switching. These techniques include, but are notlimited to loss of signal (LOS), loss of frame (LOF), signal degradation(SD). The fault detection technique can be carried out in either theelectrical or optical domain. The fault detection techniques in theoptical domain can include, but are not limited to optical power loss,optical time domain reflectometer (OTDR) measurements, loss of pilottone, or use of a dedicated port and/or wavelength.

[0035] The channel switching may occur under the control of anyappropriate control system including, but not limited to an OLXCcontroller (not shown) or a network operations center (not shown). Anadvantageous control system that may be used with the present inventionis described in the commonly-assigned U.S. patent application, Ser. No.08/936,369 (Chaudhuri) which is herein-incorporated by reference.Chaudhuri particularly describes a computer-based automatic restorationmethodology.

[0036] The control system may reside locally at one of the plurality ofnodes A, B, C, D or be remotely located and connect with one of thenodes A, B, C, D wherein both cases the control system is interconnectedto all the other nodes via data links embedded in the connectionsbetween nodes or via external data links. The data link network mayadvantageously comprise a Digital Communication Network (DCN) and/or aNetwork Operations System (NOS) which provides an ultra-reliable datanetwork for communicating status signaling messages (e.g., alarmsignals) between nodes regarding system operation, faults, etc. Also,for better reliability a redundant control system may be provided atanother location or alternatively the control system may be provided ateach node.

[0037] The control system can include a system processor for monitoringOLXC switch states and issuing switch commands. It would be apparent toone skilled in art how to design specific software and/or hardwareimplementations for addressing, monitoring, and controlling an OLXCbased on the number of ports and switch configurations.

[0038] Referring to FIG. 5, an illustrative example is described. Inresponse to a single interface failure occurring on an SP or S channelcarried by line 520 between nodes A and B, the OLXC 505 switches thechannel to an R channel on the other line 525 connecting nodes A and B.The single interface failure could comprise an OC-48 interface on theoptical layer cross-connect switch 505 or an optical transmitter orreceiver failure on the path of an SP or S channel on line 520.

[0039] In an alternate example, the entire line 520 fails due to opticalamplifier failure, a fiber cut, or some other line failure. In responseto the failure, the SP channels carried on line 520 are switched by OLXC505 to the R channels of the other line 525 linking nodes A and B. Withreference to FIG. 5, the SP channel (----) carrying service1-2-3-4-5-6-7-8 through link ABC on line 520 is switched by OLXC 505 onto R channels on line 525 such that the restored path becomes1-2-15-16-5-6-7-8 for link ABC.

[0040] However, in response to a similar line failure, S channelscarried on the failed line 520 are switched in a different manner torestore traffic carried by these channels. The S channels are restoredfrom the end nodes of the channel path. The S channel (----) carryingservice 9-17-10-11-12-13-14 through link ABC on line 520 is switched byOLXC 505 on to R channels on line 595 through link ADC such that therestored path becomes 9-17-18-19-20-21-14. This S channel restorationprocess can be advantageously implemented using the automaticrestoration scheme described in the previously mentioned Chaudhuriapplication.

[0041]FIG. 6 shows an optical fiber communication system 600 using anHPA when a failure occurs on both optical fiber lines 620, 625 betweennodes A, B. The system 600 includes OLXCs 605, 635, 660, 685 for eachnode A, B, C, D respectively. Nodes A, B, C, D comprise IEs 610, 615,630, 640, 655, 665, 680, 690 with at least two IEs for each node A, B,C, D respectively. Again, at every node, each IE includes at least twopairs of interface ports wherein one port in each pair is used forinterconnecting the IE to the OLXC while the other port in each pairinterconnects the IE to another IE at a different node. The IEs areinterconnected to the OLXCs, via OLXC equipment cards at the OLXC endand the interface ports at the IE end, through a pair of optical fibersfor carrying bidirectional traffic (e.g., OC-48 or OC-192 channels) orthrough electrical lines using optical-to-electrical transducers.Advantageously, the IEs comprise wavelength division multiplexers (WDM),preferably dense wavelength division multiplexers (DWDM).

[0042] Each IE includes a two-line optical fiber connection (link), viathe interface ports, to a separate node in the system 600 wherein lines620, 625 connect IEs 610, 630 of nodes A, B respectively, lines 645, 650connect IEs 640, 655 of nodes B, C respectively, lines 670, 675 connectIEs 665, 680 of nodes C, D respectively, and lines 695, 698 connect IEs615, 690 of nodes A, D respectively. The line connections preferablycomprise a single or multiple fiber pairs (cable bundle) connectionbetween nodes.

[0043] With reference to FIG. 3(b), another illustrative example isdescribed. In response to both lines 620, 625 on link AB failing due toa fiber cut, both the SP and the S channels are restored from the endnodes of the channel path. The SP channel (______) carrying service1-2-3-4-5-6-7-8 through link ABC on line 620 is switched by OLXC 605 onto R channels on line 695 through link ADC such that the restored pathbecomes 1-2-16-17-18-19-8. Also, the S channel (______) carrying service9-10-11-12-13-14-15 through link ABC on line 620 is switched by OLXC 605on to R channels on line 698 through link ADC such that the restoredpath becomes 9-10-20-21-22-23-15. Again, this end node channelrestoration process can be advantageously implemented using theautomatic restoration scheme described in Chaudhuri.

[0044] In this HPA protection scheme, system planning and managementhelps ensure restoration channel availability. Channel assignment of SP,S, and R channels in each line forming the internodal link arereciprocal to each other. The number of SP channels in one line must beequal to the number of R channels in the other line. The remainingchannels are assigned as S channels provided there are sufficient Rchannels in each link of the network to guarantee 100% restoration ofall SP channels when there is a line failure anywhere in the network.

[0045] This HPA restoration scheme effectively offers at least twogrades of service (at least two priority levels for restoration). Thecommunication services carried by the SP channels are as reliable orgiven as high a restoration priority level as the communication servicescarried by the two-line 1:1 protection scheme previously described.Also, the S channel communication services are as reliable or given ashigh a restoration priority level as the communication services carriedby the one-line 1:1 or 1:N protection schemes described previously.

[0046] Also, the present invention has greater capacity than an opticaltransport system using the two-line 1:1 protection scheme assuming notall channel services require the same amount of reliability. Aparticular example can be used to demonstrate this capacity gain.Assuming DWDM system channel capacity of 80 channels per line,approximately 60% of all channels (total of SP and S) on a link can bedesignated as reserved to guarantee restoration of all working trafficagainst a line failure in any link in the network. Therefore, 30channels per line are left to be designated as R channels. Of theremaining 50 channels, 30 can be designated as SP channels and 20 as Schannels. Therefore, for every two-line link, there are 60 SP channels,40 S channel used for revenue-generating traffic with two grades ofservice reliability (two priority levels for restoration). Each grade orpriority level is protected against equipment failures as well as fibercuts. The HPA carries a total of 100 working channels on the two-linelink as compared to 80 working channels in the two-line 1:1 protectionscheme since no protection capacity is used for revenue-generatingtraffic in the two-line 1:1 scheme. Therefore, the present inventionprovides a capacity-efficient architecture resulting in a 25% gain ofhighly reliable revenue-generating capacity. The 60 R channels in thetwo DWDM lines can still be used for low-priority traffic that may bepreempted in response to failure of SP and S traffic.

[0047] The present invention provides several advantages to serviceproviders of optical communication services. The hybrid protectionarchitecture described herein enables a reliable optical communicationsnetwork that provides varying grades of communication services whileimproving idle capacity utilization when restoring communicationservices on alternate optical fiber communication paths in the network.

[0048] Although the invention is described herein primarily using a meshtopology example utilizing DWDM, it will be appreciated by those skilledin the art that modifications and changes may be made without departingfrom the spirit and scope of the present invention. As such, the methodand apparatus described herein may be equally applied to any opticalcommunication system topology comprising a plurality of nodes utilizingany other architecture.

What is claimed is:
 1. An optical fiber communication system,comprising: a plurality of nodes interconnected by optical fibers, eachnode including an optical layer cross-connect switch interconnected toat least two interface elements, each interface element including atleast two optical fiber connections, and each interface elementconnecting to a separate node via said at least two optical fiberconnections; each said optical fiber connection including at least threechannel groups, at least one channel group including predeterminedchannels allocated for restoring communication in response to a failureoccurring in one of said optical fiber connections, and at least twochannel groups including predetermined channels allocated for carryinguser traffic; said optical switch being enabled for switching at least aportion of said channel groups from a first optical fiber connection toa second optical fiber connection in response to a failure occurring inthe first optical fiber connection, the second optical fiber connectionbeing enabled for carrying the same or greater capacity of informationas carried by said portion of switched channel groups in the firstoptical fiber connection.
 2. The system of claim 1, wherein: saidchannel groups including priority levels for switching said channelgroups to a second optical fiber connection in response to a failureoccurring in a first optical fiber connection carrying said channelgroups; and wherein said priority levels including at least a highestpriority level and a second highest priority level.
 3. The system ofclaim 2, wherein: said highest priority level being assigned to a superpremium channel group, and a second highest priority level beingassigned to a standard channel group.
 4. The system of claim 2, wherein:said optical switch being enabled for switching at least a portion ofsaid highest priority channel group to at least a portion of saidrestoration channels within a second optical fiber connection inresponse to a failure occurring in a first optical fiber connectioncarrying said portion of highest priority channel group.
 5. The systemof claim 4, wherein: said optical switch being further enabled forswitching at least a portion of said second highest priority channelgroup to at least a portion of said restoration channels within a secondoptical fiber connection in response to a failure occurring in a firstoptical fiber connection carrying said portion of second highestpriority channel group.
 6. The system of claim 1, wherein: saidinterface elements are wave division multiplexers.
 7. The system ofclaim 1, wherein: said restoration channel group being enabled forcarrying pre-emptable user traffic.
 8. The system of claim 1, wherein:said system having a mesh configuration.
 9. The system of claim 1,wherein: said failure is an interface element failure, optical fiberfailure, an optical amplifier failure, or an optical transceiverfailure.
 10. The system of claim 2, wherein: said switching to thesecond optical fiber connection results in a capacity gain for saidhigher priority channel groups.
 11. A method for restoring communicationin an optical fiber communication system, comprising: assigning at leastthree channel groups to each optical fiber connection in an opticalfiber communication system comprising a plurality of nodesinterconnected by optical fibers, each node including an optical layercross-connect switch interconnected to at least two interface elements,each interface element including at least two optical fiber connections,and each interface element connecting to a separate node via said atleast two optical fiber connections; switching at least a portion ofsaid channel groups from a first optical fiber connection to a secondoptical fiber connection in response to a failure occurring in the firstoptical fiber connection, the second optical fiber connection beingenabled for carrying the same or greater capacity of information ascarried by said portion of switched channel groups in the first opticalfiber connection.
 12. The method of claim 11, wherein: said step ofassigning includes designating priority levels for switching saidchannel groups to a second optical fiber connection in response to afailure occurring in a first optical fiber connection, wherein saidpriority levels including at least a highest priority level and a secondhighest priority level; and said step of switching includes switchingsaid portion of channel groups based on said designated priority levels.13. The method of claim 12, wherein: said step of designating includesassigning said highest priority level to a super premium channel group,and assigning said second highest priority level to a standard channelgroup.
 14. The method of claim 12, wherein: said step of switchingincludes switching at least a portion of said highest priority channelgroup to a portion of said restoration channels within a second opticalfiber connection in response to a failure occurring in a first opticalfiber connection carrying said portion of highest priority channelgroup.
 15. The method of claim 12, wherein: said step of switchingfurther includes switching at least a portion of said second highestpriority channel group to a portion of said restoration channels withina second optical fiber connection in response to a failure occurring ina first optical fiber connection carrying said portion of second highestpriority channel group.
 16. The method of claim 12, wherein: said stepof switching includes switching said highest priority channel groupwithin a first optical fiber connection to a portion of said restorationchannels within a second optical fiber connection in response to anoptical transceiver failure on said first optical fiber connection or afailure at an interface between an interface element and said firstoptical fiber connection, wherein both first and second optical fiberconnections are connected to said interface element at a node in saidsystem.
 17. The method of claim 12, wherein: said step of switchingincludes switching said second highest priority channel group within afirst optical fiber connection to a portion of said restoration channelswithin a second optical fiber connection in response to an opticaltransceiver failure on said first optical fiber connection or a failureat an interface between an interface element and said first opticalfiber connection, wherein both first and second optical fiberconnections are connected to said interface element at a node in saidsystem.
 18. The method of claim 12, wherein: said step of switchingincludes the steps of: switching said highest priority channel groupwithin a first optical fiber connection to at least a portion of saidrestoration channels within a second optical fiber connection inresponse to an optical amplifier failure on said first optical fiberconnection, wherein both first and second optical fiber connectionsbeing connected to a first interface element at a node in said system;and switching said second highest priority channel group within saidfirst optical fiber connection to at least a portion of said restorationchannels within a third optical fiber connection in response to saidoptical amplifier failure on said first optical fiber connection,wherein said third optical fiber connection being connected to a secondinterface element at the node in said system.
 19. The method of claim18, wherein: said highest priority channel group comprises a superpremium channel group, and said second highest priority channelcomprises a standard channel group.
 20. The method of claim 12, wherein:said step of switching includes the steps of: switching both saidhighest and second highest priority channel groups within a firstoptical fiber connection to at least a portion of said restorationchannels within a second optical fiber connection in response to anoptical fiber failure on said first optical fiber connection, whereinsaid first and second optical fiber connections being connected to firstand second interface elements, respectively, at a node in said system.21. The method of claim 20, wherein: said highest priority channel groupcomprises a super premium channel group, and said second highestpriority channel group comprises a standard channel group.
 22. Themethod of claim 11, wherein: said interface elements are wave divisionmultiplexers.
 23. The method of claim 11, wherein: said step ofswitching includes interrupting user traffic being carried by saidportion of restoration channels within the second optical fiberconnection.
 24. The method of claim 11, wherein: said system having amesh configuration.
 25. The method of claim 11, wherein: said failure isan interface element failure, optical fiber failure, an opticalamplifier failure, or an optical transceiver failure.
 26. The method ofclaim 12, wherein: said step of switching to the second optical fiberconnection results in a capacity gain for said higher priority channelgroups.